The objective of the proposed research is to determine the mechanisms which bacteria use to regulate the expression of their genes under stress conditions. Changes in the nitrogen storage polymer, cyanophycin granule polypeptide, or multi-L-arginyl poly (aspartic acid), will be studied during nitrogen starvation using non-nitrogen fixing cyanobacteria as a model system. The overall goal of research in this laboratory is to relate cell growth and physiology to environmental variables such as nutrient limitation, utilization of organic and inorganic carbon, and temperature. 15N nutrients will be used to follow the cellular path of nitrogen by measuring the 15N/14N ratio of components of CGP in order to show the course of, and the kinetics of change in, nitrogen in CGP when it is produced under various environmental conditions. 15N/14N ratios will be measured by gas chromatography/mass spectrometry (CG/MS) of CGP after its isolation from stressed cells. Mutants in cyanophycin metabolism will be isolated to begin studies on a genetic level. The study of cyanophycin metabolism will indicate the extent and types of regulatory mechanisms that exist in cases where vast compositional changes are made in cells due to growth in varying environmental conditions. Much remains to be determined about the mechanisms bacteria use to regulate the expression of their genes; such studies will have relevance to both prokaryotic cells, and the comparative study of a wide variety of microorganisms may result in a comprehensive theory of cell biology. An understanding of the regulation of nutrient stress is essential for understanding of basic cellular biology and physiology. It is also relevant to the yield improvement of cyanobacterial growth for efforts such as screening for anti-tumor and cytotoxic metabolites as well as for isolating phycobiliproteins to replace radioactive isotopes as reporters in immunoassays and other diagnostics.